U.S. patent number 8,521,354 [Application Number 12/190,354] was granted by the patent office on 2013-08-27 for diagnosis of sensor failure in airflow-based engine control system.
This patent grant is currently assigned to Southwest Research Institute. The grantee listed for this patent is Shizuo Sasaki. Invention is credited to Shizuo Sasaki.
United States Patent |
8,521,354 |
Sasaki |
August 27, 2013 |
Diagnosis of sensor failure in airflow-based engine control
system
Abstract
An air-flow based control system for an internal combustion
engine has various sensors that are used to calculate various
control commands. By comparing pairs of values calculated from
different sensors, errors in connection with the sensors can be
detected.
Inventors: |
Sasaki; Shizuo (San Antonio,
TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sasaki; Shizuo |
San Antonio |
TX |
US |
|
|
Assignee: |
Southwest Research Institute
(San Antonio, TX)
|
Family
ID: |
41681823 |
Appl.
No.: |
12/190,354 |
Filed: |
August 12, 2008 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100042284 A1 |
Feb 18, 2010 |
|
Current U.S.
Class: |
701/29.1 |
Current CPC
Class: |
F02D
41/18 (20130101); F02D 41/0072 (20130101); F02D
41/144 (20130101); F02D 41/222 (20130101); Y02T
10/47 (20130101); F02D 2200/0406 (20130101); F02D
2200/0414 (20130101); Y02T 10/40 (20130101); F02D
2041/1433 (20130101); F02D 2200/0402 (20130101) |
Current International
Class: |
G06F
7/00 (20060101) |
Field of
Search: |
;701/29,35,102,29.1,29.7,30.5 ;60/601-603 ;123/435,304 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
US. Appl. No. 11/773,784, "Combustion Control System Based on
In-Cylinder Conditions", Sarlashkar et al., 27 pages, filed Jul. 5,
2007. cited by applicant .
U.S. Appl. No. 12/134,598, "Combustion System for Internal
Combustion Engine with Rich and Lean Operating Conditions", Sasaki
et al., 56 pages, filed Jun. 6, 2008. cited by applicant.
|
Primary Examiner: Nguyen; Kim T
Attorney, Agent or Firm: Chowdhury & Georgakis, P.C.
Livingston; Ann C.
Claims
What is claimed is:
1. A method of diagnosing failure in connection with a mass airflow
sensor used in an airflow-based engine control system for an
internal combustion engine, the engine having one or more cylinders
and an exhaust gas recirculation (EGR) system that recirculates
exhaust at a variable EGR rate, comprising: obtaining a measured
airflow mass value from the mass airflow sensor; obtaining a
measured intake oxygen concentration value; obtaining a measured
exhaust oxygen concentration value; calculating an EGR rate based
on the relationship between the intake oxygen concentration value
and the exhaust oxygen concentration value; obtaining a measured
intake manifold pressure value; obtaining a measured intake
manifold temperature value; calculating a total gas flow rate into
the cylinders, based on the measured intake pressure value and the
measured intake manifold temperature value; subtracting the EGR
rate from the total gas flow rate, thereby obtaining a calculated
value for a mass air flow rate, which is not based on the measured
airflow mass value; comparing the measured airflow mass value to
the calculated airflow mass value; and generating airflow mass
sensor failure data if the comparing step does not result in a
match.
2. The method of claim 1, further comprising the steps of accessing
a mapped EGR rate from a stored EGR map, and of generating airflow
mass failure data only if the calculated EGR rate and the mapped
EGR rate are matched.
3. The method of claim 1, wherein the measured intake oxygen
concentration value is measured by a first oxygen sensor in the air
intake line and the measured exhaust oxygen concentration value is
measured by a second oxygen sensor in the exhaust line.
4. A method of diagnosing failure in connection with an intake
oxygen sensor or exhaust oxygen sensor of an engine having an
exhaust gas recirculation (EGR) system that recirculates exhaust at
a variable EGR rate, and having a control system that uses an EGR
base map to determine the EGR rate, comprising: calculating a first
calculated EGR rate by subtracting a measured intake air flow rate
from a total as flow rate into the cylinders; obtaining a measured
intake oxygen concentration value using the intake oxygen sensor;
obtaining a measured exhaust oxygen concentration value using the
exhaust oxygen sensor; calculating a second calculated EGR rate
based on the relationship between the intake oxygen concentration
value and the exhaust oxygen concentration value; accessing the EGR
base map stored in memory of the control system, the map providing
EGR rates for given engine operating conditions, such that for a
current operating condition the EGR rate provided by the map is the
EGR rate used to control the EGR rate of the engine; and comparing
the first calculated EGR rate and the second calculated EGR rate
with the EGR rate provided by the EGR base map for the same engine
speed and intake O2 mass value; and if the first calculated EGR
rate and EGR rate provided by the EGR base map match each other but
do not match the second calculated EGR rate, generating data
indicating failure of the intake oxygen sensor or the exhaust
oxygen sensor.
Description
TECHNICAL FIELD OF THE INVENTION
This invention relates to control systems for internal combustion
engines, and more particularly to diagnosing sensor failures in an
airflow-based engine control system.
BACKGROUND OF THE INVENTION
As a result of the Clean Air Act Amendments of 1990, two "tiers" of
emission standards for light-duty vehicles in the United States
were defined. These standards specifically restrict emissions of
carbon monoxide (CO), oxides of nitrogen (NOx), particulate matter
(PM), formaldehyde (HCHO), and non-methane organic gases (NMOG) or
non-methane hydrocarbons (NMHC). The Tier I standard was phased in
from 1994 to 1997. Tier II standards are being phased in from 2004
to 2009. Within the Tier II standard, there are sub-rankings
ranging from BIN 1-10.
To meet these standards, many advances have been made in engines
and their control systems. New combustion control strategies are
designed to minimize engine-out emissions and to control exhaust
gas composition and temperature for optimum operation of
post-combustion emissions control devices.
One such combustion control strategy is based on "airflow-based"
control, especially designed for diesel engines or other engines
that use direct fuel injection. "Airflow-based" control systems may
be contrasted to more conventional "fuel-based" control systems. In
fuel-based control, in response to activity of the accelerator
pedal, the engine control unit determines the quantity of fuel to
inject. Downward action of the accelerator pedal causes the engine
control unit to inject more fuel. With this type of engine control,
it is difficult to provide air-fuel ratios that are matched to
desired combustion modes.
Airflow-based control systems are also referred to as "airflow
dominant" control systems. In modern engines, the dynamics of fuel
delivery are fast and can be controlled on a cylinder-by-cylinder
basis. On the other hand, airflow is greatly affected by delays in
the exhaust gas recirculation (EGR) path and by turbocharger lag.
Airflow dynamics are slower and more difficult to control than fuel
delivery. To achieve specific air-fuel ratio targets, in airflow
dominant control systems, the fast fuel dynamics follow the slower
airflow dynamics.
Airflow based control systems require accurate sensors and airflow
models. The inputs to the control calculations include both engine
operating inputs, such as accelerator pedal position and engine
speed, as well as sensor inputs, such as airflow mass, intake
temperature, and intake pressure. Accurate control outputs, such as
commands to control fuel injection and air-handling devices,
require accurate real time input measurements.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
FIG. 1 illustrates an example of an internal combustion engine
having fuel injection and exhaust gas recirculation (EGR), and a
diagnostic unit that operates in accordance with the methods
described herein.
FIG. 2 illustrates the input measurements, input calculations, and
the calculations performed by the diagnosis unit of FIG. 1.
FIG. 3 further illustrates the diagnostic process performed by the
diagnosis unit of FIG. 1, using the inputs of FIG. 2.
FIG. 4 illustrates the calculation of the EGR rate (Method 1).
FIGS. 5-7 illustrate calibration maps used for the calculations of
FIG. 4.
FIG. 8 illustrates how the diagnostic unit is used to diagnose
failures in connection with the intake manifold O2 sensor.
FIG. 9 illustrates how the diagnostic unit is used to diagnose
failures in connection with the commanded fuel injection
quantity.
DETAILED DESCRIPTION OF THE INVENTION
The following description is directed to diagnosing sensor failures
in an airflow-based combustion control system for an internal
combustion engine. More specifically, methods are described for
diagnosing failure of various measurement devices whose
measurements are used for calculating airflow mass and the EGR
rate.
U.S. Pat. No. 7,163,007, entitled "Control System for Internal
Combustion Engine", to Sasaki, et al, assigned to Honda Motor Co.,
describes one example of an "airflow based" combustion control
system. The engine uses dilute combustion with the goal of low
engine-out emissions to minimize the required exhaust treatment.
For both lean and rich operating conditions, an estimated
in-cylinder oxygen amount (oxygen mass) is used to determine
fueling parameters. U.S. Pat. No. 7,389,173, entitled "Control
System for an Internal Combustion Engine Operating with Multiple
Combustion Modes", to Wang, assigned to Southwest Research
Institute, and U.S. patent Ser. Nos. 11/773,784, 12/061,711, and
12/134,598 also describe various airflow-based control systems and
methods.
The systems and methods of each of the above-referenced patents and
patent applications use various calculations in which fresh airflow
mass is an important control system input. Thus, each of these
patents and patent applications describe engines and control
systems with which the methods described herein may be used. Each
is incorporated herein by reference.
As indicated in the Background, in an airflow-based control system,
various engine control parameters are calculated on the basis of
the fresh airflow mass and the recirculated exhaust (EGR) flow
rate. Thus, it is important to have accurate measurement of both
flow rates.
FIG. 1 illustrates an internal combustion engine with fuel
injection, of a type with which the methods described herein may be
used. In the example of FIG. 1, engine 100 is a diesel engine.
However, the methods described herein are not limited to diesel
engines; a stratified charge engine is one example of a gasoline
engine that also uses fuel injection.
Various elements of engine 100 are known. Although not explicitly
shown, each cylinder 130 has a fuel injector. The fuel injection
quantity is determined by the engine control system, which
calculates ever-varying fuel injection quantity values and delivers
a corresponding control signal to the fuel injectors.
Turbocharger 110 has a compressor 111 and turbine 112. An example
of a suitable turbocharger is a variable geometry turbocharger
(VGT).
Engine 100 also has an EGR (exhaust gas recirculation loop), which
in the example of FIG. 1, is a high pressure loop. EGR cooler 121
cools the exhaust before it is mixed with fresh air from the
compressor 111.
Valves 130 and 150 control boosted air intake into the cylinders
and the EGR flow, respectively.
FIG. 1 further illustrates the location of various temperature and
pressure measurement sensors, for sensing T1, T2, and T3
(temperatures) and P1, P2, and P3 (pressures). Of particular
interest herein are the intake temperature and intake pressure, as
measured by sensors P1 and T1.
An O2 sensor 174 is installed to measure the O2 in the exhaust from
the exhaust manifold. A mass airflow sensor 140 measures the flow
rate of fresh air intake. Various mass airflow sensors are known
and commercially available, with measuring airflow directly and
others estimating airflow from intake pressure and other
parameters.
A combustion control unit 150, programmed to control various
combustion control parameters in accordance with the methods
described herein. Control unit 150 may be a processor-based unit
having appropriate processing and memory devices. The memory of
control unit 150 also stores various tables, which store maps of
known values to variables. Values for these tables are acquired as
described below, and then stored in control unit 150 for access
during engine operation. Control unit 150 may be integrated with or
part of a comprehensive engine control unit.
Control unit 150 is programmed to execute various airflow-based
control algorithms. As explained in the Background, this means that
engine control parameters, such as fuel quantity, EGR rates, etc.,
are calculated in response to in-cylinder conditions, including the
amount of fresh air available to the cylinders during any given
engine operating condition. For such a system, it is imperative
that these calculations be accurate.
An example of an airflow based control system is described in U.S.
Pat. No. 7,389,173, referenced above and incorporated by reference
herein. The control system uses an engine model, in which an
important control calculation is an "intake manifold fresh air
fraction", which is the ratio of fresh air from the compressor to
the amount of recirculated exhaust gas.
Another example of an airflow based control system is described in
U.S. patent Ser. No. 12/134,598 referenced above and incorporated
by reference herein. In this control system, an important control
calculation is the amount of in-cylinder oxygen mass, which is
calculated from the fresh airflow rate. Other examples and features
of airflow-based control systems are described in U.S. Pat. No.
7,389,173 and U.S. patent application Ser. Nos. 11/773,784 and
12/061,711, also referenced above and incorporated by reference
herein.
Of particular interest to this description, system 100 further has
a sensor diagnostic unit 160. Its operation is explained below, and
like control unit 150, it may be implemented with digital
processing devices and memory programmed in accordance with the
methods described herein. For use in its calculations, it receives
certain calculations as well as certain sensor outputs, as
described below.
FIG. 2 illustrates inputs and outputs of the diagnostic process
performed by diagnosis unit 160. It is used to diagnose faults in
connection with any, some or all of the following sensors and
calculations: airflow mass sensor 140, intake pressure sensor P1,
intake manifold O2 sensor 176, and EGR fouling. The specific
diagnostic methods are explained below in connection with FIGS. 3
and 8. As explained below in connection with FIG. 9, the diagnosis
unit 160 may be enhanced to also perform fuel injection quantity
correction.
As explained below, diagnostic unit 160 operates by comparing pairs
of values, with each pair being for the same parameter but derived
from different calculations or measurements. For example, for
airflow mass, there is a measured value from sensor 140 and a
calculated value based on sensors other than airflow sensor 140.
Each pair of values is compared. If the two values match (within a
specified tolerance), the sensors used to derive the values are
consistent, and no fault exists. If the values of a pair do not
match, there is a fault. The faulty sensor can then be identified
by more detailed analysis.
The method of FIG. 2 is implemented by the diagnosis unit 160 of
FIG. 1, appropriately programmed. It receives various inputs,
either calculated or measured. Specifically, it receives an airflow
mass value from an airflow sensor, such as mass airflow sensor
140.
Diagnosis unit 160 also receives intake pressure and intake
temperature values from the corresponding pressure and temperature
sensors (P1 and T1) illustrated at the intake manifold in FIG. 1.
It also receives an exhaust O2 concentration value from sensor
174.
As further explained below in connection with FIG. 3, a first set
of the diagnostic input values are used to calculate an airflow
mass value. A second set of these input values is used to calculate
a first EGR rate value. A third set of these input values is used
to calculate a second EGR rate value.
It is assumed that the diagnostic input values represent engine
conditions during the engine operating events, and in particular
during the same fuel injection event. The calculations and
estimations described herein are "real time" in the sense that they
are based on simultaneous real time measurements and calculations
and provide real time failure diagnosis.
FIG. 3 illustrates further details of the diagnostic method. The
method of FIG. 3 has two paths, one for diagnosing failure in
connection with EGR rate calculation inputs (Steps 32-35), and
another path for diagnosing failure in connection with airflow mass
sensor 140 (Steps 36-38).
Step 31 is receiving diagnostic inputs illustrated in FIG. 2. As
illustrated by the arrows in FIG. 2, certain inputs are used for
certain calculations.
Referring again to FIG. 3, Step 32 is performing a first EGR rate
calculation (Method 1). This method of calculating the EGR rate is
based on airflow mass, the intake pressure, and the intake
temperature, which are measured diagnostic inputs. This method uses
the ideal gas law applied to the intake manifold, which provides a
relationship between the EGR rate, the fresh airflow mass rate as
measured by sensor 140, and the total (EGR gas plus fresh air) gas
flow rate into the cylinders. The total gas flow rate can be
calculated from known speed density methods. Specifically, at a
given engine speed, the intake manifold pressure is almost
proportional to the total mass of in-cylinder gas. Thus, the total
in-cylinder gas mass is predictable from intake manifold pressure,
if account is taken of the effect of temperature at each engine
speed. This prediction assumes that temperature affects volumetric
efficiency at a given engine speed.
Further details of calculating the total in-cylinder gas mass are
described in U.S. Pat. No. 7,389,173, referenced above. An example
of calculating the EGR rate from airflow mass, intake pressure and
intake temperature is described in U.S. Pat. No. 7,163,007,
referenced above. FIGS. 4-7 and the accompanying text provide
further explanation of EGR rate calculations (Method 1).
Step 33 is performing a second EGR rate calculation (Method 2).
This method of calculating the EGR rate is based on the
relationship between the intake manifold O2 concentration (as
measured by sensor 176) and the exhaust O2 concentration (as
measured by sensor 174). For example: EGR
rate=(0.211-O2.sub.intake)/(0.211-O2.sub.exhaust)
Step 34 is comparing the two calculated EGR rate values. If the
values match (within a specified tolerance) there is no error in
connection with the EGR rate diagnostic inputs. If they do not
match, in Step 35, appropriate failure data is generated so that
further diagnostic analysis can be performed in connection with EGR
rate calculation inputs. More specifically, a mismatch of the
calculated values may indicate failure in connection with the
intake pressure sensor P1.
As illustrated, comparison may also be made to an EGR rate value
provided from an EGR rate base map. Such maps are often stored and
used by an engine control unit to determine EGR rates based on
current engine operating inputs. Thus, Step 34 may include
comparing either or both of the calculated EGR rates to the rate
provided by the EGR base map (referred to herein as the "mapped EGR
rate"). If the EGR rate values match, no failure is indicated. If
they do not match, EGR failure, such as EGR fouling, is indicated,
and appropriate data is generated. It is assumed that the all
comparisons are made under the same engine operating conditions,
particularly at the same engine speed and O2 mass values.
The EGR rate comparisons are between pairs of values, and depending
on which values match or do not match, different failures may be
indicated. If the two calculated EGR rates match and the mapped
value does not, EGR rate failure is indicated. If the EGR rate
(Method 1) and the mapped EGR rate match but the EGR rate (Method
2) does not, sensor failure in connection with the EGR rate (Method
2) calculations is indicated. If the EGR rate (Method 2) and the
mapped EGR rate match but the EGR rate (Method 1) does not, sensor
failure in connection with the EGR rate (Method 1) calculations is
indicated. Further analysis is used to indicate which sensor of the
diagnostic inputs may be defective.
Step 36 is calculating an airflow mass value. This value is
calculated on the basis of the EGR rate (Method 2, calculated as
described above), the intake pressure, and the intake temperature.
As stated above, the total gas flow rate into the cylinders can be
calculated from temperature and pressure measurements. This value
minus the EGR rate provides a calculated airflow rate value.
Step 37 is comparing the measured airflow mass value to the airflow
mass value calculated in Step 36. If the values match (within a
specified tolerance) there is no error in connection with the
airflow mass diagnostic inputs. If they do not match, in Step 38,
appropriate failure data is generated so that further diagnostic
analysis can be performed in connection with the airflow mass
sensor 140 or the airflow mass calculation inputs.
FIGS. 4-7 illustrate the calculation of the EGR rate (Method 1). As
stated above, the input values are airflow mass, intake manifold
pressure, intake manifold temperature, and the exhaust air/fuel
ratio. The total intake O2 mass is the sum of the air contributed
by the fresh air intake (as measured by sensor 140) and the fresh
air contributed by EGR. The total intake manifold pressure (Pin, as
measured by sensor P1) is the sum of the partial pressure
contributed by fresh air (Pa) and the partial pressure contributed
by EGR (Pe). The calculation of the EGR rate is based on the
measured pressure, airflow, and temperature values. If the EGR rate
is known, the total in-cylinder O2 mass can be calculated.
Furthermore, if the total in-cylinder O2 mass is known, the intake
manifold O2 concentration can be calculated. The exhaust A/F ratio
can be obtained in various ways, such as by comparing the O2
measured by sensor 176 to the O2 measured by sensor 174 during rich
engine operation. The exhaust A/F ratio can also be estimated
during no EGR and high load engine operation from the airflow mass
measurement from sensor 140 and the fuel injection amount as
commanded by the engine control unit.
FIGS. 5, 6, and 7 illustrate how temperature and partial pressure
(Pa) are calibrated over engine speed (rpm) and fresh air mass. In
the calibration map of FIG. 5, airflow mass (Ga), intake manifold
pressure (Pin), intake manifold temperature (Tin), and O2 intake
(O2in) are calibrated over engine torque and engine speed (rpm). In
the calibration maps of FIGS. 6 and 7, partial pressure from fresh
air (Pa) and intake manifold temperature (Tin) are calibrated over
airflow mass (Ga) and engine speed (rpm).
Details of a suitable method for estimating in-cylinder O2 (intake
O2) are described in U.S. Pat. No. 7,163,007, referenced above.
Referring again to FIG. 3, it should be understood that diagnosis
unit 160 could be programmed to perform either or both of these
diagnostic paths. In other words, diagnosis unit 160 could be
programmed to detect failure in connection with EGR rate
calculations, airflow mass calculations, or both. The particular
diagnostic inputs needed for each EGR rate and airflow mass
calculations are described below. If only airflow mass sensor
failure is being diagnosed (Steps 36-38), either of the EGR rate
calculations (Step 32 or Step 35), or some other EGR rate input,
could be used.
As stated above and as illustrated in FIG. 8, the measured and
calculated inputs of FIG. 2 may also be used to diagnose failure in
connection with intake manifold 02 sensor 176. This method involves
the calculations described above in connection with FIG. 4.
Step 91 is receiving values for airflow mass (measured by sensor
140), and for intake temperature and pressure (measured by sensors
T1 and P1). Step 92 is calculating the EGR rate using Method 1
explained above in connection with FIG. 3, Step 32. Step 93 is
calculating an intake O2 mass value, which is calculated without
use of the intake manifold O2 sensor and based on the calculated
EGR rate. Step 94 is calculating the intake manifold O2
concentration, based on the results of the above steps. Step 95 is
comparing the measured and calculated intake manifold O2
concentration values. If there is a match, no sensor failure is
indicated. However, if the values do not match, a failure in
connection with sensor 176 is indicated, and appropriate data is
generated in Step 95.
FIG. 9 illustrates how the diagnostic unit illustrated in FIGS. 1
and 2 may be enhanced to diagnose fuel injection quantity errors.
Step 101 is receiving a current fuel injection quantity (mass)
valve from the control unit 150.
Step 101 may be performed using these input values: intake manifold
O2 concentration (from sensor 176), exhaust O2 concentration (from
sensor 174), EGR rate (calculated as described in Method 1 or
Method 2 of FIG. 3), and airflow mass (from sensor 140). Using
these input values: Fuel inj
mass=(O2.sub.intake-O2.sub.exhaust)/(28.96*1-EGR
rate)*(12+(H/C)/1+(H/C)/4)*airflow mass, where H/C is the
hydrogen-carbon ratio of the fuel. In Step 103, the two fuel
injection quantity values are compared. If the two values match, no
error or fault is indicated. If they do not match, a fuel quantity
injection error is indicated, and in Step 104, appropriate data is
generated.
* * * * *